The present invention relates generally to nickel-base alloys. In particular, the present invention relates to nickel-base alloys that can be affordable and can exhibit superior temperature capability and comparable processing characteristics relative to certain nickel-based superalloys, such as the well-known Alloy 718, versions of which are available from Allegheny Ludlum Corporation, Pittsburgh, Pa., and Allvac, Monroe, N.C. under the names Altemp(copyright) 718 and Allvac(copyright) 718 alloys, respectively. The present invention is also directed to a method of making a nickel-base alloy and an article of manufacture that includes a nickel-base alloy. The nickel-base alloy of the present invention finds application as, for example, components for gas turbine engines, such as disks, blades, fasteners, cases, or shafts
The improved performance of the gas turbine engine over the years has been paced by improvements in the elevated temperature mechanical properties of nickel-base superalloys. These alloys are the materials of choice for most of the components of gas turbine engines exposed to the hottest operating temperatures. Components of gas turbine engines such as, for example, disks, blades, fasteners, cases, and shafts all are fabricated from nickel-base superalloys and are required to sustain high stresses at very high temperatures for extended periods of time. The need for improved nickel-base superalloys has resulted in many issued patents in this area, including, for example, U.S. Pat. Nos. 3,046,108; 4,371,404; 4,652,315; 4,777,017; 4,814,023; 4,837,384; 4,981,644; 5,006,163; 5,047,091; 5,077,004; 5,104,614; 5,131,961; 5,154,884; 5,156,808; 5,403,546; 5,435,861 and 6,106,767.
In many cases, improved performance is accomplished by redesigning parts so as to be fabricated from new or different alloys having improved properties (e.g., tensile strength, creep rupture life, and low cycle fatigue life) at higher temperatures. The introduction of a new alloy, however, particularly when introduced into a critical rotating component of a gas turbine engine, can be a long and costly process and may require a compromise of certain competing characteristics.
Alloy 718 is one of the most widely used nickel-base superalloys, and is described generally in U.S. Pat. No. 3,046,108. Alloy 718 has a typical composition as illustrated in the table below.
The extensive use of Alloy 718 stems from several unique features of the alloy. Alloy 718 has high strength, along with balanced creep and stress rupture properties up to about 1200xc2x0 F. (649xc2x0 C.). While most high strength nickel-base superalloys derive their strength by the precipitation of xcex3xe2x80x2 phase, with aluminum and titanium being major strengthening elements, i.e., Ni3(Al, Ti), Alloy 718 is strengthened mainly by xcex3xe2x80x3 phase with niobium, i.e. Ni3Nb, being a major strengthening element and with a small amount of xcex3xe2x80x2 phase playing a secondary strengthening role. Since the xcex3xe2x80x3 phase has a higher strengthening effect than xcex3xe2x80x2 phase at the same volume fraction and particle size, Alloy 718 is generally stronger than most superalloys strengthened by xcex3xe2x80x2 phase precipitation. In addition, xcex3xe2x80x3 phase precipitation results in good high temperature time-dependent mechanical properties such as creep and stress rupture properties. The processing characteristics of Alloy 718, such as castability, hot workability and weldability, are also good, thereby making fabrication of articles from Alloy 718 relatively easy. These processing characteristics are believed to be closely related to the lower precipitation temperature and the sluggish precipitation kinetics of the xcex3xe2x80x3 phase associated with Alloy 718.
At temperatures higher than 1200xc2x0 F. (649xc2x0 C.), however, the xcex3xe2x80x3 phase has very low thermal stability and will rather rapidly transform to a more stable xcex4 phase that has no strengthening effect. As a result of this transformation, the mechanical properties, such as stress rupture life, of Alloy 718 deteriorate rapidly at temperatures above 1200xc2x0 F. (649xc2x0 C.). Therefore, the use of Alloy 718 typically is limited to applications below 1200xc2x0 F. (649xc2x0 C.).
Due to the foregoing limitations of Alloy 718, many attempts have been made to improve upon that superalloy. U.S. Pat. No. 4,981,644 describes an alloy known as the Rene"" 220 alloy. Rene"" 220 alloy has temperature capabilities of up to 1300xc2x0 F. (704xc2x0 C.), or 100xc2x0 F. (56xc2x0 C.) greater than Alloy 718. Rene"" 220 alloy, however, is very expensive, at least partly because it contains at least 2 percent (typically 3 percent) tantalum, which can be from 10 to 50 times the cost of cobalt and niobium. In addition, Rene"" 220 alloy suffers from relatively heavy xcex4 phase content, and only about 5% rupture ductility, which may lead to notch brittleness and low dwell fatigue crack growth resistance.
Another nickel-base superalloy, known as Waspaloy(copyright) (a registered trademark of Pratt and Whitney Aircraft) nickel-base superalloy (UNS N07001), available from Allvac, Monroe, N.C., is also widely used for aerospace and gas turbine engine components at temperatures up to about 1500xc2x0 F. (816xc2x0 C.). This nickel-base superalloy has a typical composition as illustrated in the table below.
While Waspaloy nickel-base superalloy possesses superior temperature capability compared to Alloy 718, it is more expensive than Alloy 718, resulting, at least partly, from increased amounts of the alloying elements nickel, cobalt, and molybdenum. Also, processing characteristics, such as hot workability and weld ability, are inferior to those of Alloy 718, due to strengthening by xcex3xe2x80x2, leading to higher manufacturing cost and more limited component repairability.
Thus, it is desireable to provide an affordable, weldable, hot workable nickel-base alloy that has high temperature capability greater than that of Alloy 718.
According to one particular embodiment of the present invention, the nickel-base alloy comprises, in weight percent: up to about 0.10 percent carbon; about 12 up to about 20 percent chromium; 0 up to about 4 percent molybdenum; 0 up to about 6 percent tungsten, wherein the sum of molybdenum and tungsten is at least about 2 percent and not more than about 8 percent; about 5 up to about 12 percent cobalt; 0 up to about 14 percent iron; about 4 percent up to about 8 percent niobium; about 0.6 percent up to about 2.6 percent aluminum; about 0.4 percent up to about 1.4 percent titanium; about 0.003 percent up to about 0.03 percent phosphorous; about 0.003 percent up to about 0.015 percent boron; nickel, and incidental impurities. According to the present invention, the atomic percent of aluminum plus titanium is from about 2 to about 6 percent, the atomic percent ratio of aluminum to titanium is at least about 1.5; and/or the sum of atomic percent of aluminum plus titanium divided by the atomic percent of niobium equals from about 0.8 to about 1.3. The present invention relates to nickel-base alloys characterized by including advantageous levels of aluminum, titanium and niobium, advantageous levels of boron and phosphorous, and advantageous levels of iron, cobalt and tungsten.
The present invention also relates to articles of manufacture such as, for example, a disk, a blade, a fastener, a case, or a shaft fabricated from or including the nickel-base alloy of the present invention. The articles formed of the nickel-base alloy of the present invention may be particularly advantageous when intended for service as component(s) for a gas turbine engine.
Furthermore, the present invention relates to a nickel-base alloy comprising, in weight percent: 0 up to about 0.08 percent carbon, 0 up to about 0.35 percent manganese; about 0.003 up to about 0.03 percent phosphorous; 0 up to about 0.015 percent sulfur; 0 up to about 0.35 percent silicon; about 17 up to about 21 percent chromium; about 50 to about 55 percent nickel; about 2.8 up to about 3.3 percent molybdenum; about 4.7 percent up to about 5.5 percent niobium; 0 up to about 1 percent cobalt; about 0.003 up to about 0.015 percent boron; 0 up to about 0.3 percent copper; and balance being iron (typically about 12 to about 20 percent), aluminum, titanium and incidental impurities, wherein the sum of atomic percent aluminum and atomic percent titanium is from about 2 to about 6 percent, the ratio of atomic percent aluminum to atomic percent titanium is at least about 1.5, and the sum of atomic percent of aluminum plus titanium divided by the atomic percent of niobium equals from about 0.8 to about 1.3.
The present invention also relates to a method for making a nickel-base alloy. In particular, according to such method of the present invention, a nickel-base alloy having a composition within the present invention as described above is provided and is subject to processing, including solution annealing, cooling and aging. The alloy may be further processed to an article of manufacture or into any other desired form.